Ferromagnetic Stability Research Articles

Doping enhanced ferromagnetism and induced half-metallicity in CrI3 monolayer

Two-dimensional materials are of current great interest for their promising applications to postsilicon microelectronics. Here we study, using first-principles calculations and a Monte Carlo simulation, the electronic structure and magnetism of CrI3 monolayer, whose bulk material is an interesting layered ferromagnetic (FM) semiconductor. Our results show that CrI3 monolayer remains FM with , and the FM order is due to a superexchange in the near-90° Cr-I-Cr bonds. Moreover, we find that an itinerant magnetism could be introduced by carriers doping. Both electron doping and hole doping would render CrI3 monolayer half-metallic, and steadily enhance the FM stability. In particular, hole doping is three times as fast as electron doping in increasing TC, and a room temperature FM half-metallicity could be achieved in CrI3 monolayer via a half-hole doping. Therefore, CrI3 monolayer would be an appealing two-dimensional spintronic material.

A comparative study on ferromagnetic C/O-implanted GaN films by positron annihilation spectroscopy

Room temperature ferromagnetism was observed in both C- and O-implanted GaN films, which were irradiated by 80keV C/O-ions with respective dose of 5×1016 and 2×1017ions/cm2. Positron annihilation spectroscopy was used to explore the magnetic origin and the correlation between the magnetism and structural features. The results reveal that carbon-ions play an important role in the stable ferromagnetism in C-implanted GaN films, while oxygen has no effect on the magnetic properties, even than a weak hysteresis loop was observed in O-implanted sample. This weak ferromagnetism is demonstrated as originated from Ga-related vacancies which induced by implantation. With first-principle calculations, we confirmed that substitutional C-ion at N-site can introduce magnetic moment for 0.8μB and stabilize ferromagnetic coupling with adjacent Ga-vacancy at room temperature. Moreover, the effect of O-ions was clearly ruled out. Our discussion gives an experimental and theoretical insight of the different origin of ferromagnetism between acceptor and donor non-metal-doped GaN materials.

Changing the magnetic and optical properties of (Ga, Fe)N and (Ga, Co)N by alloying with oxygen

Systematic density functional theory studies and model analyses have been used to show that the magnetic properties of (Ga0.94Fe0.06)N and (Ga0.94Co0.06)N can be changed from disorder local moment state to ferromagnetic state by replacing ~2 % of the nitrogen atoms with oxygen atoms. The estimated curie temperatures are much higher than the room temperature which indicates the room temperature ferromagnetism can be realized by oxygen doping. Moreover, the optical absorption spectra obtained by ab initio calculations confirm the ferromagnetic stability based on the charge state of magnetic impurities. (Ga0.94Fe0.06)N0.98O0.02 and (Ga0.94Co0.06)N0.98O0.02 ferromagnetic DMS exhibits half-metallic behavior, which is suitable for spintronics applications.

Unusual Dirac half-metallicity with intrinsic ferromagnetism in vanadium trihalide monolayers

Monolayer vanadium trihalides show stable 2D intrinsic ferromagnetism, half-metallicity and Dirac point.

Antisite disorder study by Monte Carlo simulation of the double perovskite Sr2CrReO6

In the last few years there has been a growing interest in the double perovskite (DP) Sr2CrReO6, as a magnetic material used in spintronics, due to its high Curie temperature (TC=610K). Antisite disorder is a defect that affects the spin polarization and the Curie temperature of all PDs. We conducted this work by Monte Carlo simulation to study the effect of the antisite disorder on this compound for two cases: Cr-excess expressed by Sr2Cr1+xRe1−xO6 and Re-excess expressed by Sr2Cr1−xRe1+xO6. This simulation has transformed the concept of the antisite conceived as defect, into a tool to explain the role of transition metals, namely Cr and Re, in the stability and the magnetic performance of the compound Sr2CrReO6. This simulation allows positioning the Cr as a key element in determining the high Curie temperature and the ferromagnetic stability. The effect of crystal field of Re in the disordered sublattice regarding the disorder rates was also explored.

The effect of fluorine doping on electronic structure and ferromagnetic stability of Os-doped TiO2 rutile phase: First-principles calculations

We have investigated the effect of fluorine doping on electronic structure and ferromagnetic stability of Os-doped TiO2 rutile using the first-principles calculations within generalized gradient approximation. We find that Ti14Os2O32 is half metallic ferromagnetic with homogenous of physical properties in different directions of osmium, but the obtained results show that the antiferromagnetic order is energetically much favored relative to the ferromagnetic order in all the considered directions. The addition of fluorine in this system plays an important role in the stability of the ferromagnetic state. Indeed, the Ti14Os2O30F2 compound presents a high electronic concentration at the Fermi level. In fact, the F-dopant behaves as an n-donor and introduces an extra electron in the system with 100% spin polarization of the conduction electrons crossing the Fermi level.

Ferromagnetism of wide-bandgap semiconductor surfaces: Mg-doped AlN

The surface magnetism of Mg-doped AlN is investigated by the first-principles method. All studied surfaces, whether they are non-polar, polar or semi-polar, favor a ferromagnetic ground state, which is stabilized by the virtual charge hopping between partially filled states of MgN clusters. However, the stability of ferromagnetism varies from surface to surface owing to the interplay among the localization of magnetic moments, energy level splitting, and sp–p interaction between MgN clusters. Among the various surfaces being studied, the Mg-doped AlN surface is expected to be ferromagnetic at room temperature as a result of its strong localization of defect states.

Predicted ferromagnetic insulator CrO2/TiO2 superlattice with the modified Becke–Johnson potential

The ferromagnetic insulator plays a major role in high-performance spintronic applications. So, it is very necessary to search for better ferromagnetic insulators that are compatible with current semiconductor technology. We investigate the electronic structures and magnetic properties of the superlattice by using Tran and Blaha’s modified Becke and Johnson exchange potential. The calculated results show that the superlattice is a ferromagnetic insulator, which combines ferromagnetic properties of with insulating properties of . The ferromagnetic stability is proven by magnetic energy differences for a series of lattice constants a. It is very interesting that both the majority-spin channel and spin non-conservation gaps firstly decrease with increasing lattice constants a, and then increase. However, the minority-spin channel gap firstly decreases, then remains nearly steady. These trends of gaps can be understood by changes of electronic band structures. If the superlattice was experimentally synthesized with ferromagnetic insulator properties, it should be used to design high-performance spintronic devices, achieving new functionality.

The Magnetism Behavior of Fe0.93V0.02Cr0.05S2 Pyrite Within Ab Initio Calculation

The Korringa-Kohn-Rostoker approximation method combined with coherent potential approximation (KKR-CPA) and the parameterization of Vosko, Wilk, and Nusair (VWN) for ab initio calculations have been used to study the magnetism impacts of the vanadium-and-chromium-doped and vanadium-and-chromium-co-doped FeS2 pyrite. Our results show that the antiferromagnetic (AFM) stability belongs to super-exchange coupling type and then to the existing disordered local moment (DLM) in Fe0.98V0.02S2. However, Fe0.95Cr0.05S2 shows that the ferromagnetic (FM) stability belongs to double-exchange coupling type and is having a considered Curie temperature (TC) which leads to significant magnetic proprieties. Moreover, 3d-3d hybridization of transition metals shows that is believed to result half-metal proprieties for the Fe0.93V0.02Cr0.05S2 system, so V and Cr could be interacting with 3p orbital of S. As a result, this forms the p-d orbital hybridization producing an efficient magnetic moment field to line up the V and Cr magnetic moment and stabilizing the half-metallic (FM) state, beside having a high magnetic moment and an evaluated useful TC in eventual spintronic applications.

Stabilization of weak ferromagnetism by strong magnetic response to epitaxial strain in multiferroic BiFeO3.

Multiferroic BiFeO3 exhibits excellent magnetoelectric coupling critical for magnetic information processing with minimal power consumption. However, the degenerate nature of the easy spin axis in the (111) plane presents roadblocks for real world applications. Here, we explore the stabilization and switchability of the weak ferromagnetic moments under applied epitaxial strain using a combination of first-principles calculations and group-theoretic analyses. We demonstrate that the antiferromagnetic moment vector can be stabilized along unique crystallographic directions ([110] and [–110]) under compressive and tensile strains. A direct coupling between the anisotropic antiferrodistortive rotations and the Dzyaloshinskii-Moria interactions drives the stabilization of the weak ferromagnetism. Furthermore, energetically competing C- and G-type magnetic orderings are observed at high compressive strains, suggesting that it may be possible to switch the weak ferromagnetism “on” and “off” under the application of strain. These findings emphasize the importance of strain and antiferrodistortive rotations as routes to enhancing induced weak ferromagnetism in multiferroic oxides.

Contrasting magnetism in dilute and supersaturated cobalt–fullerene mixture films

The combination of cobalt with nanocarbons promises hybrid nanostructures that are ideal for the development of memory storage and spin-transfer electronics. Here, we report a dramatic effect of composition on the magnetic properties of the CoxC60 mixtures, whose nanostructure was organized upon simultaneous deposition and sequential exposure to air. We assert a critical change in the mixture’s organization yielding either the composite nanostructure as array of the Co/CoO core–shell nanoparticles (NPs) in the C60-based matrix at a high content of Co (a supersaturated mixture or SSM) or a coexistence of fcc-C60 and CoaC60 fulleride when the Co content x is lower than some critical value (an ultradilute mixture or UDM). Magnetization of the SSM composite exhibits a superparamagnetic effect caused by the small Co/CoO NPs. Similar magnetization of the UDM with revealed a stable ferromagnetism and evidenced the formation of a magnetic Co2C60 fulleride. Phase composition in the UDM and SSM films was verified with the XRD and Raman spectra. The UDM and SSM films reveal great difference in content of the remaining oxygen which implies easy diffusion of O2 molecules within the C60-based phases and their splitting at the Co NP surface followed by formation of CoO shells. The results obtained indicate controlled access to a variety of promising Co–C60 magnetic nanostructures.

Half-Metallic Properties in the New Ti2NiB Heusler Alloy

The electronic structure and magnetic properties of the new Ti2NiB Heusler alloy, which has a high-ordered CuHg2Ti structure, were examined using the self-consistent full-potential linearised augmented plane wave method within density functional theory. Analysis of the electronic band structures and state densities of the Ti2NiB full-Heusler compound revealed that whereas the spin-up electrons are metallic, the spin-down bands are characterised by a gap of 0.62 eV, resulting in stable half-metallic ferromagnetism with a magnetic moment of 3 μ B/f.u. The total magnetic moment (M t) and number of valence electrons (Z t) in the Ti2NiB compound were found to obey the Slater-Pauling (SP) rule of M t = Z t − 18. Due to their different surroundings, the magnetic moments of Ti (1) and Ti (2) exhibit distinct differences, with the magnetic contribution of Ti (1) slightly larger than that of Ti (2). A negative formation enthalpy value was also obtained, thus encouraging the experimental manufacture of the alloy. The band gap was elucidated to be mainly determined by the bonding and antibonding states created from the hybridisations of the d states between the Ti (1)-Ti (2) coupling and the Ni atom. Finally, the Ti2NiB compound was found to maintain 100 % polarisation at the Fermi level, with the half-metallic character present for lattice constants ranging from 5.60 to 6.50 A, thus making the alloy favourable for practical applications.

Half-Metallicity Ferromagnetism in Half-Heusler XCaZ (X = Li, Na; Z = B, C) compounds: an Ab Initio Calculation

The search for ferromagnetic semiconductors and stable half-metallic ferromagnets remains a high priority in solid-state physics. A general understanding of structure–property relationships is a necessary prerequisite for the design of new materials. In this study, the band structures and magnetic properties of the form XCaZ (Y = Ca) compounds in the half-Heusler structure have been calculated with the full-potential linear augmented plane wave (FP-LAPW) method within the spin density functional theory. The calculations reveal that the nonmagnetic element can induce stable ferromagnetic state in alkaline metals. The most stable atomic arrangement is when XCaZ occupy the (0, 0, 0), (1/4, 1/4, 1/4) and (3/4, 3/4, 3/4) positions. For the majority spin channel the Fermi level is located in the band gap, and for the minority spin there is no energy gap around the Fermi level, which gives a direct evidence of the half-metallic behavior.

Rapid degradation of methylene blue in a novel heterogeneous Fe3O4 @rGO@TiO2-catalyzed photo-Fenton system.

Herein, a ternary nanocomposite with TiO2 nanoparticles anchored on reduced graphene oxide (rGO)-encapsulated Fe3O4 spheres (Fe3O4@rGO@TiO2) is presented as a high efficient heterogeneous catalyst for photo-Fenton degradation of recalcitrant pollutants under neutral pH. Fe3O4@rGO@TiO2 was synthesized by depositing TiO2 nanoparticles on the surface of the Fe3O4 spheres wrapped by graphene oxide (GO) which was obtained by an electrostatic layer-by-layer method. This as-prepared catalyst reflected good ferromagnetism and superior stability which makes it convenient to be separated and recycled. Due to the synergic effects between the different components composed the catalyst, swift reduction of Fe3+ can be achieved to regenerate Fe2+. Fe3O4@rGO@TiO2 exhibited enhancing catalytic activity for the degradation of azo-dyes compared with Fe3O4, Fe3O4@SiO2@TiO2 or SiO2@rGO@TiO2, further conforming the rapid redox reaction between Fe2+ and Fe3+. All these merits indicate that the composite catalyst possesses great potential for visible-light driven destruction of organic compounds.

A stable 4f half-metallic ferromagnetism Eu4O3N predicted from GGA+U calculations

Objective: Half-metallic ferromagnetism plays a major role in high-performance spintronic applications due to its 100% spin-polarization. So, it is very necessary to search better half-metallic ferromagnets with large magnetic moment and being compatible with current semiconductor technology.Methods: We study cubic Eu4O3N on the basis of state-of-the-art first-principles calculations by using generalized gradient approximation plus U method.Results: It is found that the Eu4O3N is a half-metallic ferromagnet with a half-metallic gap of 376meV and the large Eu ion magnetic moment up to about 7μB. The structural and ferromagnetic stability are proved by mechanical stability criterion and magnetic energy differences, respectively. The half-metallic properties are also stable against the isotropic strain, volume-conservative tetragonal strain and rhombohedral distortion. For the choice of U between 4 and 8eV, the Eu4O3N still is half-metallic ferromagnet.Conclusion: This provides a new idea for searching new half-metallic ferromagnetism by f electrons.Practical implications: If the Eu4O3N was experimentally synthesized with half-metallic properties, it should be used to design high-performance spintronic devices.

Magnetic properties of manganites doped with gallium, iron, and chromium ions

The magnetization and the crystal structure of the La0.7Sr0.3Mn1 − xMxO3 (M = Ga, Fe, Cr; x ≤ 0.3) systems are studied. The substitution of gallium and chromium is shown to cause phase separation into antiferromagnetic and ferromagnetic phases, whereas the substitution of iron for manganese stabilizes a spinglass state. The ferromagnetic phase in the chromium-substituted compositions is much more stable than that in the case of substitution by iron ions or diamagnetic gallium ions. The magnetic properties are explained in terms of the model of superexchange interactions and the localization of most eg electrons of manganese. The stabilization of ferromagnetism in the chromium-substituted compositions can be caused by the fact that the positive and negative contributions to the superexchange interaction between Mn3+ and Cr3+ ions are close to each other but the antiferromagnetic part of the exchange is predominant. Moreover, some chromium ions are in the tetravalent state, which maintains the optimum doping conditions.

Magnetism, electronic structure and half-metallic property of transition metal (V, Cr, Mn, Fe, Co) substituted Zn3P2 dilute magnetic semiconductors: An ab-initio study

Abstract The ab-initio electronic structure calculations are used to investigate the half-metallic property, structural stability, spin dependent density of states and magnetism of transition metal (V, Cr, Mn, Fe, Co) substituted Zn 3 P 2 . Our results show the half-metallic ground state and ferromagnetic (antiferromagnetic) stability for small concentrations (2.5% and 5%) of transition metal atom substitution considered in our study. The structural and magnetic stability of the substituted compounds have been investigated through the calculation of the heat of formation and analyzing the minimum total energies corresponding to the ferromagnetic, antiferromagnetic and nonmagnetic phases. The substituted transition metal atom is found to give rise to magnetism of these compounds and half-metallic property is observed in many cases. We have used the spin, orbital and atom projected density of states to investigate this point and studied the nature of bonding in these systems using the charge density contours. We have observed from our calculations, magnetically stable phases and large values of the magnetic moments in these compounds and it suggests that these compounds may be useful materials for semiconductor spintronic devices. We have further calculated the theoretical X-ray diffraction pattern of these compounds.

Reduction of defect-induced ferromagnetic stability in passivated ZnO nanowires**Project supported by the National Natural Science Foundation of China (Grant Nos. 11474165, 21203096, and 11204137), the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20130031, BK20131420, and BK2012392), and the Fundamental Research Funds for the Central Universities of China (Grant No. 30920130111016).

First-principles calculations are performed to study the electronic structures and magnetic properties of ZnO nanowires (NM). Our results indicate that the single Zn defect can induce large local magnetic moment (∼ 2μ B) in the ZnO NWs, regardless of the surface modification. Interestingly, we find that local magnetic defects have strong spin interaction, and favor room-temperature ferromagnetism in bared ZnO NW. On the other hand, although H passivation does not destroy the local magnetic moment of Zn vacancy, it does greatly reduce the spin interaction between magnetic defects. Therefore, our results indicate that H passivation should be avoided in the process of experiments to maintain the room-temperature ferromagnetism.

Tailoring the structural and magnetic properties of Cu-doped ZnO by ±bc-axis pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 51031004 and 51272078), the Natural Science Foundation of Guangdong, China (Grant No. S2012010008124), the National Basic Research Program of China (Grant No. 2015CB921202), the Project for Guangdong Province Universities and Colleges Pearl River Scholar Funded Scheme (2014),

The structural and magnetic properties of the Cu-doped ZnO (ZnO:Cu) under c-axis pressure were studied using first-principle calculations. It was found that the ZnO:Cu undergoes a structural transition from Wurtzite to Graphite-like structure at a c-axis pressure of 7–8 GPa. This is accompanied by an apparent loss of ferromagnetic stability, indicating a magnetic transformation from a ferromagnetic state to a paramagnetic-like state. Further studies revealed that the magnetic instability is closely related to the variation in crystalline field originated from the structural transition, which is in association with the overlapping of spin–charge density between the Cu2+ and adjacent O2-.

Giant magnetization canting due to symmetry breaking in zigzag Co chains on Ir(001)

We demonstrate a canted magnetization of biatomic zigzag Co chains grown on the (5 × 1) reconstructed Ir(001) surface using density functional theory (DFT) calculations and spin-polarized scanning tunneling microscopy (SP-STM) experiments. It is observed by STM that biatomic Co chains grow in three different structural configurations. Our DFT calculations show that they are all in a ferromagnetic (FM) state. Two chain types possess high symmetry due to two equivalent atomic strands and an easy magnetization direction that is along one of the principal crystallographic axes. The easy magnetization axis of the zigzag Co chains is canted away from the surface normal by an angle of 33°. This giant effect is caused by the broken chain symmetry on the substrate in combination with the strong spin–orbit coupling of Ir. SP-STM measurements confirm the stable FM order of the zigzag chains with a canted magnetization.